We? I tip 20%, rounding slightly up. I have never worked as a waiter, but I did several turns as a busboy, getting a cut from the waiters' tips. I'm not out to impress waitresses, I'm not out to make a statement that affects somebody's main source of income; this is financial. (I once tipped damned near 50%, but that was after I took four fourth grade boys to lunch on one's birthday, and they left a very messy table; that wasn't a reward, but an apology.)
"Quality of service has a laughably small impact on tip size."
Quite. See above. I'm not going to penalize the wait staff for what might be the faults of the kitchen.
A few weeks ago, I had beers on a couple of occasions at a hotel bar in Boston. There the "gratuity" was included in the charge, and that was fine with me.